Spoilers ahead for Tuesday's season finale of Agents of S.H.I.E.L.D.
This week's season finale of Agents of S.H.I.E.L.D. climaxed in an epilogue in which John Hannah's Dr. Holden Ratcliffe was constructing something he called an "LMD" - a term that should be familiar to longtime readers of Marvel Comics.
But what is a LMD? The better question may be who is an LMD? LMD stands for "Life Model Decoy," a kind of robotic clone that usually operates as a secret surrogate for a real person. A user can see, hear, speak through, and control the actions of a LMD, allowing them to go unnoticed for an extended length of time, even years and decades even.
Many prominent Marvel characters have used LMD's, but perhaps the most famous is Nick Fury. LMD's are S.H.I.E.L.D. tech, and though they've been used by non-S.H.I.E.L.D. members, Fury is notorious for sending an LMD to do his dirty work. He's used them so often to hide in plain sight, that there's even an enhanced version of one of his LMD's that gained its own consciousness and operated as a villain under the name Max Fury. In Original Sin, it was revealed that the real Fury hadn't been seen in years, and was living in space, much older than anyone knew.
LMD's have often been used to replace prominent people in the Marvel Universe without their consent or knowledge as well. A villain named Father replaced Eric O'Grady, the third Ant-Man, with an LMD after O'Grady was killed. Likewise, Fury himself replaced his old ally and best friend Dum Dum Dugan with an LMD that, according to Original Sin, operated for many years in the Marvel Universe with no one the wiser - least of all Dugan himself.
Tony Stark and Maria Hill have also used LMD's to operate in unsafe or surreptitious situations, while "Thunderbolt" Ross used one to disguise his transformations into Red Hulk.
LMD's have showed up in the Marvel Cinematic Universe before - sort of. In The Avengers, Tony Stark tells Coulson he's speaking to the "Life Model Decoy of Tony Stark," but this was a throwaway line, and actual LMD's haven't appeared yet (that we know of, anyway - that's kind of the point). This did lead to speculation that either Coulson or Fury - who both "died" in the MCU and returned - would turn out to be LMD's, but so far, Agents of S.H.I.E.L.D. is the first official appearance of an actual LMD in MCU continuity.
And according to the show's co-showrunner Jed Whedon, LMD's have been something that his team has wanted to use for years.
"Partially, we’ve been waiting on it because we knew what was coming in the second Avengers movie so he didn’t want to hit that note before them," the co-showrunner told Variety, referring to his brother Joss Whedon's Avengers: Age of Ultron.
The closest approximation to what he could be referring to is the Vision, a synthetic human created in a lab and subverted by Ultron in the movie. The Vision's body was created by Helen Cho (played by actress Claudia Kim) using a device called the Cradle at the U-GIN Genetic Research Facility in Seoul. At the end of the movie, Cho was brought to work at the new Avengers Facility with a team of scientists.
Cho's character and her technology haven't been mentioned in any subsequent Marvel Cinematic Universe movies or television series.